It's now Sunday. Holden buys a children's record for Phoebe and thinks about how Phoebe always understands what he's really saying. While passing a church he overhears a poor little boy singing, "If a body catch a body coming through the rye." The boy's voice and innocent image makes him happy. He calls Jane, but hangs up when her mother answers.
Holden's thoughts about Phoebe and joy at the young boy's song indicate Holden's idealization of the purity of childhood. This feeling of purity makes him feel able to call Jane, but he still can't deal with the adult world.
Holden buys theater tickets for his date with Sally, even though he hates actors in particular and dislikes the theater in general.
Holden hates things that aren't what they seem, including actors.
Holden then heads over to the Mall, a part of the park where Phoebe often roller-skates on Sundays. He meets a girl who thinks Phoebe's at the Museum of Natural History with her class. Though it soon becomes clear that the class trip was Saturday, Holden walks to the museum anyway. Holden thinks about how comforting it is that the museum's displays are frozen in time. He says you can always go back to the museum and discover that the only thing that has changed is you yourself.
Holden, who fears and hates adulthood, likes things that don't change. The museum displays fit this description. They stop time, just as Allie's death froze Allie in the ideal state of childhood.
But when Holden arrives at the museum he finds he doesn't want to go inside. He takes a cab to meet Sally Hayes instead.
Holden fears going into the museum just as he fears calling Jane. He's protecting his illusions.